Rick wrote:
Base spreading resistance can be overcome by using a sufficiently high source impedance
This sounds like the all-too-common noise figure fallacy (increasing input impedance to get a lower NF). All this does is raise the source impedance's contribution to the total noise -- it doesn't reduce the amplifier input noise voltage, and it increases the amplifier noise due to input noise current. The result is more output noise, not less, and a reduced signal to noise ratio, despite the improved NF.
Even if you use a transformer to raise the source impedance, the signal voltage increases by the turns ratio while the impedance increases by the square of the turns ratio (thus, the output noise due to the amplifier input noise current flowing through the source impedance also increases as the square of the turns ratio).
Best regards, Charles _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
